The invention relates to a coupling device with two coupling members, which are to be connected coaxially together, and a tension rod, which can be inserted into clamping elements, connected to the first coupling member, and which can be coupled to the second coupling member, which exhibits an axial passage borehole.
In the coupling device, disclosed in the document EP-A-255042 (U.S. Pat. No. 4,855,558), the end of the tension rod that is opposite the head can be coupled to the second coupling member by means of a bayonet locking mechanism. Furthermore, there are clamping elements, which act on the head of the coupling member relative to the first coupling member in order to stay the two coupling elements. In another case, where the second coupling member exhibits very little space to form the bayonet locking mechanism, the entire end of the tension rod can be tightly screwed together with the second coupling member in that a thread, formed on the end, engages with a counter thread, provided on the second coupling member.
The aforementioned coupling devices are mounted on the machining head of a machine tool, thus for example a lathe or an erosion machine, and serve to clamp a workpiece to be machined in a position at the machining head that is clearly defined spatially. The second coupling member can be either the workpiece itself or a workpiece holder, to which the workpiece is attached. Aligning passage boreholes through the tension rod and the second coupling member serve to guide the rinse fluid to the machining station.
The clamping elements are normally housed in the machining head, to which the first coupling member is permanently connected, and envelop in most cases a ball lock, whose balls, which can be moved radially to a limited degree and are distributed in the circumferential direction, engage radially, following the insertion of the tension rod, with the head of the machining head.
When the second coupling element is axially clamped to the first, cross forces are generated that become a noticeable disturbing factor when an attempt is made to obtain a positioning accuracy in an order of magnitude of one xcexcm or less, especially when the axial length of the tension rod is relatively short and, therefore, there is inadequate space for the bayonet locking mechanism.
Therefore, the invention provides members of solving on the problem for the aforementioned coupling device that will minimize the effect of the cross forces on the positioning of the second coupling member.
The invention also provides that for the purpose of reaching through the second coupling member the tension rod exhibits a shaft, whose diameter is less than the clear width of the passage borehole and whose end is radially expanded by more than the clear width. This avoids the disturbing effect on the axial and angular positioning of the second coupling member caused by, for example, cross forces, generated by the clamping elements. For example, the radial clearance allows the tension rod to deflect a little sideways from the center axis (Z axis) so that the cross forces, causing this deflection, will have no effect on the clamping process.
It has been found advantageous for the passage borehole to be enlarged by boring, thus forming an annular shoulder, in order to receive the expanded end of the tension rod. Furthermore, it is expedient for the expanded end to be designed as a separate stopper, which is connected, e.g. can be screwed, to the shaft.
Even though it is sufficient for the purpose of the invention that the annular shoulder of the second coupling member and the related contact surface on the stopper extend at right angles to the center axis, it is possible for the stopper to rest with its entire surface against the shoulder if in an improvement of the invention both the annular shoulder and the contact surface are shaped like an arch or a crown, whereby the center of curvature of the convexity of both surfaces lies on the center axis outside the tension rod.
In an especially expedient embodiment of the invention both the peripheral surface of the stopper and the opposite internal contour of the enlarged boring exhibit the same noncircularity, thus guaranteeing that there will be no torsional strain between the stopper and the second coupling element.
Furthermore, it is recommended to insert between the head of the tension rod and its end a sleeve, penetrated by the shaft with a radial clearance. Thus the guiding of the tension rod into the clamping elements is improved. If the sleeve is provided with a radial ring seal, it also serves to cut off the pressure medium, actuating the clamping elements. Furthermore, it is recommended to provide on the free front face of the sleeve at least one axially extending shaped part, for example along the line of a protruding nose or a groove-shaped depression, which finds its counter-shaped part in the free front face of the second coupling member and guarantees that the second coupling member will rest against the sleeve so as not to rotate.
To guarantee the radial motion of the tension rod relative to the second coupling member, in particular when an electrode is attached to the second coupling member, it is also recommended in an improvement of the invention that the electrode-sided opening of the passage borehole be closed at least temporarily by means of a cover, which can be locked expediently into a depression in the second coupling member.
Preferred embodiments of the invention are disclosed in the dependent claims.